Printed circuit board and manufacturing method thereof

ABSTRACT

A printed circuit board which is thin and incorporates a large-capacitance capacitor function and a manufacturing method thereof is disclosed. The printed circuit board manufacturing method includes the steps of: forming inner layer conductor circuits  32 A on a core substrate  30 ; forming a recess part  31  on the core substrate  30 ; housing, in a recess part  31 , a planar capacitor device  20  that is not resin molded and has electrodes on the surfaces on a shared side; interposing the same between insulator resin  43  and conductor metal foil  44  to heat pressurize the same for forming a multi-layer plate; forming via holes  41 A for electrically connecting an outer layer conductor circuit  42 A to the electrodes  21,22  of the capacitor device  20 ; forming a conductor layer on them; and forming the outer layer conductor circuits  42 A on the surfaces of the multi-layer plate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board and amanufacturing method thereof. More specifically, the present inventionrelates to a multi-layer printed circuit board incorporating a capacitorfunction and a manufacturing method thereof.

2. Description of Related Art

With the higher performance of electronic equipment, the number of partsmounted on a printed circuit board is being increased. Due to theminiaturization of electronic equipment, the size of the printed circuitboard is required to be further reduced. The area on which the parts canbe mounted is being made smaller.

With reduction of the parts in size, the density of surface mounting isbecoming higher due to microfabrication of the conductor pattern of theprinted circuit board.

The increased number of leads of mounted parts, smaller pitch, increasedwiring resistance with a higher multi-layer printed circuit board due toa growing number of mounted parts and finer lines, signal delay due tocross talk noise, heat generation, and malfunction of the equipment withthese become problems.

To solve these problems, the wiring length of parts need to be reduced.Specifically, there are proposed a method of burying the parts into aprinted circuit board as well as of mounting the parts on the surface ofthe printed circuit board, and a method of incorporating a functionequal to that of the parts into a printed circuit board using a highdielectric sheet material having a high dielectric constant and a pastematerial. Such techniques disclosed in Japanese Published UnexaminedPatent Application Nos. 2002-100875 and Hei 6(1994)-69663 are known.

According to the above related art, the formation of a recess part onthe printed circuit board to incorporate a smaller chip part thereintois proposed. At present, the printed circuit board is required to bethinner. Although the chip part is being made smaller, its thicknesscannot be sufficiently small, obstructing making the printed circuitboard thinner.

The smaller chip reduces the capacitance of a capacitor. It is difficultto respond to a request to make the capacitance larger.

SUMMARY OF THE INVENTION

The present invention solves the foregoing problems and provides aprinted circuit board which is thin and incorporates a large-capacitancecapacitor function and a manufacturing method thereof.

According to the present invention, a capacitor not resin molded isburied into a recess part formed on a core substrate. Alarge-capacitance capacitor can be incorporated into a thin printedcircuit board.

According to the present invention, a printed circuit boardmanufacturing method includes the steps of: forming inner layerconductor circuits on a core substrate; forming a recess part on thecore substrate; housing, in the recess part, a capacitor device notresin molded; forming insulator layers and conductor layers on the coresubstrate housing the capacitor device to form a multi-layer plate;forming via holes for electrically connecting an outer conductor layerand electrodes of the capacitor device to form a conductor layerthereon; and forming the outer layer conductor circuits on the surfacesof the multi-layer plate.

According to a preferred embodiment, the capacitor device has a planarshape, and anode and cathode electrodes are formed on the surfaces onthe shared side.

The size of the recess part is adjusted to be slightly larger than thatof the capacitor not resin molded to obtain high part positioningaccuracy. The resin for fixing parts do not need to be filled in therecess part, thereby reducing the number of processes.

Preferably, in the printed circuit board, an unmolded and unpackagedcapacitor device having a thickness of 300 μm or less is used as acapacitor part to be buried. The unpackaged capacitor device is thinnerthan the molded chip part. In the case of burying a chip part having thesame capacitance, the printed circuit board can be thinner. The printedcircuit board having the same thickness can incorporate alarge-capacitance capacitor.

Preferably, in the printed circuit board, the capacitor device to beburied in which the electrode portions are subject to copper plating orfixed copper foil having a thickness of 10 to 30 μm and surfaceroughness is optimized for bonding to the resin is used. The thicknessof the electrode portions is 10 to 30 μm. When using a laser for formingvia holes for connecting the electrodes to the conductor pattern of anupper layer, the via holes can be formed without damaging theelectrodes. The surface roughness of the electrodes is optimized forbonding to the resin. No processes for increasing the bonding to theresin are necessary. The general printed circuit board manufacturingprocess can be performed from laser beam machining to plating.

Preferably, the electrodes of the buried capacitor device are connectedto the conductor pattern of the upper layer by the via holes. When theconductor pattern of the upper layer is an outer layer of the printedcircuit board, the surfaces of the via holes filled by electrolyticcopper plating or conductive paste are flat. Since their surfaces areflat, no voids are caused in solder used for connection to the partsmounted on the surface of the printed circuit board, enablinghigh-reliability connection.

According to of the present invention, a capacitor device has adielectric layer formed on at least one side of a planar metalsubstrate, an anode electrode formed on the dielectric layer, and acathode electrode formed via a conductive film on the dielectric layer,wherein the anode electrode and the cathode electrode have a planarstructure facing toward the shared side, and resin molding is not given.The capacitor device which is relatively simple in structure and whichis preferable for thinning can be easily housed in the recess part ofthe core substrate to achieve thinning of the multi-layer plate.

According to the present invention, it is possible to obtain a thinnerprinted circuit board by burying a planar capacitor device not resinmolded into a recess part formed on a core substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the structure of a printedcircuit board according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view showing the structure of a capacitordevice according to an embodiment;

FIG. 3 is a diagram showing a printed circuit board manufacturingprocess according to an embodiment;

FIG. 4 is a diagram showing a printed circuit board manufacturingprocess according to an embodiment;

FIG. 5 is a diagram showing a printed circuit board manufacturingprocess according to an embodiment;

FIG. 6 is a diagram showing a printed circuit board manufacturingprocess according to an embodiment;

FIG. 7 is a diagram showing a printed circuit board manufacturingprocess according to an embodiment;

FIG. 8 is a diagram showing a printed circuit board manufacturingprocess according to an embodiment;

FIG. 9 is a diagram showing a printed circuit board manufacturingprocess according to an embodiment; and

FIG. 10 is a cross-sectional view showing the structure of a capacitordevice according to another embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The structure of a printed circuit board according to an embodiment ofthe present invention will be described below with reference to thedrawings. FIG. 1 shows the cross section of a printed circuit board.

A printed circuit board has an unpackaged capacitor device 20, a coresubstrate 30 housing the capacitor device, and buildup layers 40A and40B. The core substrate 30 has a recess part 31 housing the unpackagedcapacitor device 20 and plural conductor layers 32A, 32B, 32C, and 32Don the surfaces and inside thereof. The buildup layer 40A is formed withvia holes 41A and a conductor circuit 42. The conductor circuit 32A onthe surface of the core layer, the unpackaged capacitor device 20, and aconductor circuit 42A of the buildup layer are connected by via holes41A. The buildup layer 40B is formed with via holes 41B and a conductorcircuit 42B. The conductor circuit 32D on the surface of the core layeris connected to the conductor circuit 42B of the buildup layer.

According to this embodiment, the buildup layers 40A and 40B are eachformed of one layer. They can also be formed of plural buildup layers.

As shown in FIG. 2, the capacitor device 20 is a planar capacitor notresin molded and has anode electrodes (first electrodes) 21L and 21Rformed over a metal substrate 23 via a dielectric layer 24 and a cathodeelectrode (a second electrode) 22 formed over the dielectric layer 24via a conductive polymer film 25.

The metal substrate 23 is a metal substrate of aluminum, tantalum, andniobium. The dielectric oxide film layer 24 of valve action metal isformed on the surface of the substrate 23. The anode electrodes 21L and21R, the conductive polymer film 25, and the cathode electrode 22 areformed successively on the oxide film layer 24. The cathode electrode 22is formed of a graphite layer, a silver paste layer, and a copper metalplate, or of two layers of a graphite layer and a metal plating layer.Alternatively, it may be formed of a metal plating layer without agraphite layer.

The first electrodes 21 and the second electrode 22 are each formed of acopper metal having a thickness of 10 to 30 μm in which surfaceroughness is optimized for bonding to the resin. Laser beam machiningfor forming the via holes 41A on the first electrodes 21 and the secondelectrode 22, as shown in FIG. 1, is easy. Its connect ability ishigher. The bonding properties to the buildup layer 40A are increased.

The first electrodes 21 and the second electrode 22 are electrodeshaving a planar structure. As shown in FIG. 1, the via holes 41A can beeasily formed to the electrodes 21 and 22.

In the capacitor device 20 shown in FIG. 2, the first electrodes 21 andthe second electrodes 22 are formed on both sides (upper and lowersurfaces) of the planar base metal 23. Only the upper side is connectedto the via holes 41A. As shown in FIG. 10, the electrodes 21 and 22 maybe formed on one side of the capacitor device.

According to the embodiment shown in FIG. 1, the via holes are connectedto the first electrodes 21L and 21R. The via corresponding to thethickness and size of the unpackaged capacitor device. As indicated bythe dotted line of FIG. 5, the recess part 31 housing the capacitordevice having a outer dimension of the capacitor device of +200 μm orless and a depth of +50 μm or less is formed on the core layer 30.

In FIG. 6, after arranging the capacitor device 20 in the recess part31, sheet-like interlayer insulator resin 43 and copper foil 44 arestacked on both sides of the core layer. The interlayer insulator resin43 softened by press heating is filled in the recess part 31 by vacuumpressurization. The surface of the stacked printed circuit board isflattened. According to this embodiment, although the interlayerinsulator resin 43 without any metal layers is stacked, resin copperfoil can be also used.

In FIG. 7, a CO2 laser is used to hole the via holes 41A having adiameter of 0.08 to 0.15 mm reaching the first electrodes 21L and 21Rand the second electrode 22 of the capacitor device 20 and the conductorcircuits 32A and 32D of the surfaces of the core layer in the builduplayers 40A and 40B. A drill is used to hole a through hole 45 having adiameter of 0.15 to 1.0 for the through hole in the core substrate 30and the buildup layers 40A and 40B.

In FIG. 8, desmearing is performed to remove any laser beam machinedresidue on the first electrodes 21L and 21R and the second electrode 22of the capacitor device 20 and the conductor circuits 32A and 32D on thesurfaces of the core layer exposed by the CO2 laser beam machining.Electroless copper plating and electric copper plating are performed toform a copper film 50 having a thickness of 20 to 30 μm.

According to this embodiment, a plating solution for via filling is usedfor electric copper plating to flatten the surfaces of the via holes byelectric copper plating. Resin filling is performed after the electricplating to flatten the surfaces of the via holes. In this case, thefilled resin is exposed on the via holes. When performing solderedconnection, the electric copper plating needs to be performed againafter the resin filling.

In FIG. 9, a photosensitive dry film resist is laminated on the surfaceof the multi-layer plate to place a photo mask for exposure. Thendevelopment and etching are performed to form the outer layer conductorcircuits 42A and 42B for removing any conductor such as copper foil ofthe unnecessary portion.

As described above, a printed circuit board incorporating a capacitorfunction can be fabricated. It is possible to prevent the increasednumber of leads of mounted parts, an IC with a small pitch, finepatterning due to a growing number of parts, increased wiring resistancewith a higher multi-layer printed circuit board, and signal delay due tocross talk noise, heat generation, malfunction, and lack in thesurface-mounted area. The surfaces of the via holes connected to thesurface of the printed circuit board are flat. Thereforehigh-reliability connection to the surface-mounted parts is enabled.

The unmolded and unpackaged capacitor device having a thickness of 300μm or less is used as the capacitor part to be buried, so the printedcircuit board can be thinner. The large-capacitance capacitor can beincorporated, allowing the number of parts to be reduced.

The electrode portions of the unpackaged capacitor device to be buriedare subject to copper plating having a thickness of 10 to 30 μm in whichsurface roughness is optimized for bonding to the resin. The differencein thickness between the anode portion and the cathode portion is 50 μmor less. The via hole formation is easy and stable. Accordinglyhigh-reliability connection is enabled, and the contact of theunpackaged capacitor device to be buried to the insulator resin is high.

1-6. (canceled)
 7. A multi-layer printed circuit board manufacturingmethod, comprising the steps of: forming circuit patterns on conductorsof a core substrate having conductor layers; forming a recess part onthe core substrate; housing, in the recess part, a capacitor device notresin molded; forming insulator layers and conductor layers on the coresubstrate housing the capacitor device to form a multi-layer plate;forming via holes for electrically connecting an outer conductor layerof the multi-layer plate to electrodes of the capacitor device to form aconductor layer on the via holes; and forming conductor circuit patternson the surfaces of the multi-layer plate.
 8. The multi-layer printedcircuit board manufacturing method according to claim 7, wherein thecapacitor device that has a planar shape and is formed with anode andcathode electrodes on the surfaces on a shared side is buried into therecess part.
 9. The multi-layer printed circuit board manufacturingmethod according to claim 7, wherein an unpackaged capacitor device thathas a thickness of 300 μm or less is buried into the recess part. 10.The multi-layer printed circuit board manufacturing method according toclaim 8, wherein a capacitor device in which the surfaces of the anodeand the cathode are subject to copper plating having a thickness of 10to 30 μm and the difference in thickness between the anode and thecathode is 50 μm or less is buried into the recess part.
 11. Themulti-layer printed circuit board manufacturing method according toclaim 8, wherein via holes connecting an outer layer circuit pattern toelectrodes of a buried capacitor are filled with copper plating orcopper plating and conductive paste so that the surfaces thereof areflat.
 12. A multi-layer printed circuit board fabricating methodcomprising the steps of: forming a recess part on a core substratehaving conductor layers; housing, in the recess part, a planar capacitordevice that is not resin molded and is formed with anode and cathodeelectrodes on the surfaces on a shared side; forming insulator layers onthe core substrate housing the capacitor device; forming a surfaceconductor layer on the insulator layer; forming via holes forelectrically connecting the surface conductor layer to the electrodes ofthe capacitor device; and forming a conductor layer on the via holes tobe conducted to the surface conductor layer.
 13. The multi-layer printedcircuit board fabricating method according to claim 12, wherein a sheetmember having interlayer insulator resin and a metal film is stacked onthe core substrate housing the capacitor device, and the interlayerinsulator resin is softened by heating to fill the insulator resinsoftened by vacuum pressurization in the recess part, and the surface ofthe stacked printed circuit board is formed to be flattened.
 14. Amulti-layer printed circuit board manufactured by the method accordingto claim
 12. 15-20. (canceled)